Dc plasma control for electron enhanced material processing

ABSTRACT

Systems and methods for material processing using wafer scale waves of precisely controlled electrons in a DC plasma is presented. The anode and cathode of a DC plasma chamber are respectively connected to an adjustable DC voltage source and a DC current source. The anode potential is adjusted to shift a surface floating potential of a stage in a positive column of the DC plasma to a reference ground potential of the DC voltage/current sources. A conductive plate in a same region of the positive column opposite the stage is used to measure the surface floating potential of the stage. A control loop can be activated throughout various processing steps to maintain the surface floating potential of the stage to the reference ground potential. A signal generator referenced to the ground potential is capacitively coupled to the stage to control a surface potential at the stage for provision of kinetic energy to free electrons in the DC plasma.

CROSS REFERENCE TO RELATED APPLICATIONS

This patent application is a divisional application of U.S. patentapplication Ser. No. 17/524,330, filed on Nov. 11, 2021, the disclosureof which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

The present disclosure generally relates to systems and methods forproducing operating conditions in a DC plasma reaction chamber used formaterial processing, in particular, for material processing using waferscale waves of precisely controlled electrons in a DC plasma at roomtemperatures (or other temperatures if desired).

BACKGROUND

Fabrication of, for example, integrated circuits, may include processingof corresponding substrates within a (direct-current) DC plasma reactionchamber wherein electrons and/or ions are accelerated towards thesurface of the substrate to initiate a reaction that physicallytransforms the surface of the substrate. In some cases, and mainly dueto their relatively smaller mass of electrons compared to ions,substrate processing via electrons may be preferred so as to reduce anydamage to the surface of the substrate beyond the targeted physicalalterations expected by the processing step per se.

In some cases, plasma processing may include arrangement of thesubstrate in a region of the DC plasma reaction chamber such that anexact value of a surface floating potential of the substrate is notknown. Accordingly, any externally applied bias signal to the substratemay impart an energy to free electrons in a region of the plasma closeto the surface of the substrate that may not correlate to the electronenergy thresholds/levels of (atoms) materials present at the surface ofthe substrate. Teachings according to the present disclosure produceoperating conditions in the DC plasma chamber that allow for precisecontrol of the energy of the free electrons to specifically targetelectron energy thresholds of the materials present at the surface ofthe substrate.

SUMMARY

Systems and methods for material processing using wafer scale waves ofprecisely controlled electrons in a DC plasma at room temperatures (orother temperatures if desired) are presented. In the present disclosuresuch material processing is referred to as electron enhanced materialprocessing (EEMP) which allows precise control of the kinetic energy offree electrons in the DC plasma to exactly (and selectively) targetenergy levels of atoms at the surface of a substrate being processed.

According to one embodiment the present disclosure, a direct-current(DC) plasma system for processing of a substrate is presented, the DCplasma system comprising: a DC plasma reaction chamber configured tocontain a DC plasma that is generated between an anode and a cathode ofthe DC plasma reaction chamber; an adjustable DC voltage source havingan output that is electrically coupled to the anode; a DC current sourcethat is electrically coupled to the cathode; and a substrate supportstage arranged in a region of the DC plasma reaction chamber thatcontains a positive column of the DC plasma, wherein the adjustable DCvoltage source and the DC current source are electrically coupled to areference ground, and wherein during a processing step of the substrate,the adjustable DC voltage source adjusts an electrical potential at theanode to set a floating potential at a surface of the substrate supportstage to a potential of the reference ground.

According to a second embodiment of the present disclosure, a method forprocessing a surface of a substrate is presented, the method comprising:placing a substrate support stage in a region of a DC plasma reactionchamber configured to produce a positive column of the DC plasma;generating a DC plasma by coupling an adjustable DC voltage source and aDC current source respectively to an anode and a cathode of the DCplasma reaction chamber; based on the generating, producing a floatingpotential at a surface of the substrate support stage; adjusting apotential at the anode via the adjustable DC voltage source whilemaintaining via the DC current source a constant DC current between theanode and the cathode; and based on the adjusting and the maintaining,setting the floating potential to a specific potential of a referenceground of the adjustable DC voltage source.

Further aspects of the disclosure are shown in the specification,drawings and claims of the present application.

BRIEF DESCRIPTION OF DRAWINGS

The accompanying drawings, which are incorporated into and constitute apart of this specification, illustrate one or more embodiments of thepresent disclosure and, together with the description of exampleembodiments, serve to explain the principles and implementations of thedisclosure.

FIG. 1A shows a simplified schematic view of a DC plasma reactionchamber that can be used in a DC plasma processing system.

FIG. 1B shows a graph representative of a variation in (electric)potential of the plasma during operation of the DC plasma reactionchamber of FIG. 1A.

FIG. 1C shows a simplified schematic view of a DC plasma processingsystem comprising a (substrate) stage arranged in a region of the DCplasma reaction chamber of FIG. 1A.

FIG. 1D shows an exemplary biasing of the stage of the DC plasmaprocessing system of FIG. 1C via an external biasing signal generator.

FIG. 1E shows an exemplary biasing signal generated by the externalbiasing signal generator of FIG. 1D and a corresponding potentialgenerated at the surface of the stage.

FIG. 1F shows exemplary energy levels of atoms at a surface of thestage.

FIG. 2A shows a simplified schematic view of a DC plasma processingsystem according to an embodiment of the present disclosure comprisingmeans to control a surface potential of the stage.

FIG. 2B shows graphs representative of control of the surface potentialof the stage for the DC plasma processing system of FIG. 2A.

FIG. 2C shows graphs representative of adjusting the surface potentialof the stage to a reference ground potential for the DC plasmaprocessing system of FIG. 2A

FIG. 3A shows a simplified schematic view of a DC plasma processingsystem according to an embodiment of the present disclosure comprisingmeans to control a surface potential of the stage and means to measurethe surface potential.

FIG. 3B shows a simplified schematic view of a DC plasma processingsystem according to an embodiment of the present disclosure that isbased on the system of FIG. 3A with added means for automatic control ofthe surface potential.

FIG. 4A shows a simplified schematic view of a DC plasma processingsystem according to an embodiment of the present disclosure that isbased on the system of FIG. 3B with added means for biasing of thestage.

FIG. 4B shows an exemplary biasing signal provided to the stage of theDC plasma processing system of FIG. 4A and a corresponding potentialgenerated at the surface of the stage.

FIG. 4C shows exemplary energy levels of atoms at a surface of thestage.

FIG. 5 is a process chart showing various steps of a method according toan embodiment of the present disclosure for processing a surface of asubstrate.

Like reference numbers and designations in the various drawings indicatelike elements.

DETAILED DESCRIPTION

FIG. 1A shows a simplified schematic view of a prior art(direct-current) DC plasma reaction chamber (110) that can be used in aDC plasma processing system. Biasing of the DC plasma reaction chamber(110) may be provided by a DC voltage source (150) coupled between ananode, A, and a cathode, C, of the DC plasma reaction chamber (110).During operation, a glow discharge (plasma) may be formed in the chamber(110) based on interaction of a gas and electrons of a current thatflows between the anode, A, and the cathode, D. This in turn producesfree ions and electrons in the chamber (110). The principle of operationof such DC plasma reaction chamber (110) is well known to a personskilled in the art and therefore related details are omitted in thepresent disclosure.

As shown in FIG. 1A, the glow discharge formed in the chamber (110) mayinclude glow regions (G1, G2, G3, G4) that emit significant light, anddark regions (D1, D2, D3, D4) that may not emit light. Such regions mayrepresent different operating characteristics of the DC plasma reactionchamber (110), including, for example, temperature and electricpotential.

FIG. 1B shows a graph representative of a variation in the (electric)potential, V_(PP), of the plasma along an axial direction (direction oflongitudinal extension), X, of the chamber (110) during operation. Asshown in FIG. 1B, the plasma potential, V_(PP), varies from a value,V_(C), that represents the potential applied to the cathode, C, by theDC voltage source (150 of FIG. 1A), to a value, V_(A), that representsthe potential applied to the anode, A, by the DC voltage source (150 ofFIG. 1A). It should be noted that as shown for example in FIG. 1D laterdescribed, generally the value, V_(A), is at zero volts (e.g., referenceground) and the value, V_(C), is negative (e.g., in a range of about 0(zero)-500 volts).

With continued reference to FIG. 1B, abrupt variation of the potential,V_(PP), in the regions (e.g., D1, G1, D2) close to the cathode, C, andin the regions (e.g., G4) close to the anode, A, may correspond toregions of higher operating temperatures of the chamber (110). On theother side, the region G3, also known as the positive column, is aregion of quasi uniform/constant potential, V_(PP), and of loweroperating temperature. For example, considering a segment [X_(G31),X_(G32)] along the axial direction, X, of the chamber (110) that asshown in FIG. 1B is contained within the positive column region, G3, avariation of the plasma potential, V_(PP), across such segment [X_(G31),X_(G32)] is minimal, or in other words, the potential, V_(PP), acrossthe segment [X_(G31), X_(G32)] may be considered as constant.Accordingly, as shown in FIG. 1B, the plasma potential, V_(PP), acrossthe segment [X_(G31), X_(G32)] may be considered as equal to a valueV_(G3). The lower operating temperature and the constant potential valueof the plasma in the positive column region, G3, allow use of suchregion for processing of substrates as shown in FIG. 1C and FIG. 1D.

FIG. 1C shows a simplified schematic view of a DC plasma processingsystem (100C) comprising a (substrate) stage, S, arranged in thepositive column region, G3, of the DC plasma reaction chamber (110). Thestage, S, may be designed to support a flat substrate, and therefore mayinclude a top flat/planar surface. The stage, S, shown in FIG. 1C iselectrically isolated (not connected to any external electric potential)and therefore, and as known to a person skilled in the art, in thepresence of the plasma potential, V_(PP), a potential, V_(S), developsat the surface of the stage, S, that is referred to as the surfacefloating potential, V_(FP). The relationship of the (surface) floatingpotential, V_(FP), to the plasma potential, V_(PP), is shown FIG. 1C. Inparticular, as shown in FIG. 1C, the plasma potential, V_(PP), at aregion [X_(G31), X_(G32)] of the chamber (110) where the stage, S, isarranged is equal to V_(G3), and the floating potential, V_(FP), islower than (negative with respect to) the plasma potential V_(G3).

The floating potential, V_(FP), shown in the graph of FIG. 1C can beattributed to the “plasma sheath” that develops in the presence of thestage, S. As known to a person skilled in the art, at the wall or anybarrier within the plasma, a negative potential develops with respect tothe bulk of the plasma. Consequently, an equilibrium potential dropdevelops between the bulk of the plasma and the wall or barrier. Suchpotential drop is confined to a small region of space next to the wallor barrier due to the charge imbalance that develops between the plasmaand the wall or barrier. This layer of charge imbalance has a finitethickness, characterized by the Debye Length, and is called the “plasmasheath” or “sheath”. The thickness of such a layer is several Debyelengths thick, a value whose size depends on various characteristics ofthe plasma. If the dimensions of the bulk plasma (e.g., chamber 110) aremuch greater than the Debye length, for example, then the Debye lengthdepends on the plasma temperature and electron density. In theparticular case of the DC plasma operating conditions supported by theteachings according to the present disclosure (e.g., EEMP system nearroom temperature to moderately above room temperature), the Debye lengthis in the order of several millimeters (e.g., less than 10 millimeters),and the difference between the potentials V_(G3) and V_(FP) is in theorder of several volts (e.g., less than 10 volts). It should be notedthat the plasma sheath may develop in the presence of any wall orbarrier, whether conductive or not. Accordingly, once a substrate(whether conductive or insulating) is placed atop the stage, S, the samefloating potential, V_(FP), as described above with reference to FIG. 1Cmay develop at the surface of the substrate.

FIG. 1D shows an exemplary biasing of the stage, S, of the DC plasmaprocessing system of FIG. 1C via an external biasing signal generator(180) that is capacitively coupled to the stage, S, by a capacitorC_(S). In the exemplary configuration (100D) shown in FIG. 1D, thepotential, V_(A), applied to the anode, A, is at zero volts (e.g.,coupled to the reference ground, Gnd). Furthermore, as shown in FIG. 1D,a biasing signal, V_(B), applied to the stage, S, by the externalbiasing signal generator (180) may be referenced to the reference groundpotential, Gnd. Although in some prior art implementations the biasingsignal, V_(B), may be DC coupled to the stage, S, teachings according tothe present disclosure strictly prohibit such DC coupling to the stageso as to avoid a discharge path for a DC current through anyintermediate points in the chamber (110), as such discharge path maysubstantially change operating conditions within the chamber (110).

In the DC plasma processing system shown in FIG. 1D, the biasing signal,V_(B), may be used to control a potential (e.g., surface potentialV_(S)) seen by free electrons and/or ions in the vicinity of the stage,S, or of the substrate when present. Accordingly, energy of the freeelectrons and/or ions may be controlled to levels required forprocessing of the substrate. For example, as shown in the left-sidegraph of FIG. 1E, the biasing signal, V_(B), generated by the externalbiasing signal generator (e.g., 180 of FIG. 1D) may start from zero andreach in a short period of time (represented by a leading edge slope) avoltage amplitude, V_(B1). When the voltage amplitude, V_(B1), isapplied (e.g., AC coupled) to the stage, S, during a processing step (a)as shown in the top right-side graph of FIG. 1E, the voltage amplitude,V_(B1), gets added (or subtracted if negative) to the surface floatingpotential, V_(FPa), to generate a surface potential, V_(S), at thevicinity of the stage, S. However, because the free electrons and/orions are at the plasma potential, V_(PPa), only a portion of the surfacepotential, V_(S), that is above the plasma potential, V_(PPa), is seenby the free electrons and/or ions. For example, as shown in the topright-side graph of FIG. 1E, the (kinetic) energy of the free electronsand/or ions may be based on a potential differenceV_(KEa)=(V_(B1)−ΔV_(FPa)), with ΔV_(FPa), =(V_(PPa)−V_(FPa)).

On the other hand, considering a processing step (b) represented by thebottom right-side graph of FIG. 1E, which may have operating conditionsthat are different from the operating conditions of the processing step(a), including for example, a different plasma potential, V_(PPb), or adifferent floating potential, V_(FPb), that may cause a differentdifferential ΔV_(FPb), =(V_(PPb)−V_(FPb)), then for the same appliedvoltage amplitude, V_(B1), a different (kinetic) energy of the freeelectrons and/or ions is obtained. Teachings according to the presentdisclosure either eliminate variations in the operating conditionswithin the chamber (e.g., 110 of FIG. 1D), and/or compensate for suchvariations such as to allow, for example, precise control of the energyof the free electrons (and/or ions). It should be noted that variationin the operating conditions may be expected in view of different typesof processing (e.g., (a) and (b) of FIG. 1E) performed within thechamber (110), including for example, etching of a substrate withdifferent reactive gasses, cleaning of a substrate or any other processthat may alter and/or remove composition/material from the surface ofthe substrate. It should be noted that, as known by a person skilled inthe art, the different operating conditions for performing the differenttypes of processing may further include corresponding variations and/oradjustments to any one of the DC plasma current, temperature, gasmixture or flow rate within the chamber (110).

When a substrate is placed atop the surface of the stage, S, the kineticenergy of the free electrons and/or ions acquired through theapplication of the bias signal, V_(B), described above may acceleratethe free electrons and/or ions towards the surface of the substrate andcollide with the substrate to release the kinetic energy onto atoms atthe surface of the substrate. Those atoms however are at an energy levelthat is based on the potential within which they reside, or in otherwords, based on the floating potential, V_(FP). Various energy levels ofone such atom for the processing type (a) described above with referenceto FIG. 1E are shown in FIG. 1F, including the energy level, E_(n), of anucleus of an atom at the surface of the substrate, the energy level,E_(B), of an electron bound to the nucleus of an atom at the surface ofthe substrate, and the energy level, E_(e), of an electron at the orbitof an electron bound to a nucleus at the surface of the substrate.

As can be seen in FIG. 1F, the energy level, E_(n), of the nucleus is atthe (negative) potential, V_(FPa), and the energy level, E_(e), of theelectron is at the (negative) potential (E_(n)+E_(B)). In other words,in order to excite the atom to a level that breaks the bond between theelectron and the nucleus, an energy equal to, or greater than, theenergy level, E_(e), of the electron must be imparted onto the atom.Accordingly, considering a plasma processing only via the freeelectrons, the kinetic energy of the free electrons provided throughapplication of the bias signal, V_(B), represented in FIG. 1F by thepotential difference V_(KEa)=(V_(B1)−ΔV_(FPa)) must be equal to, orgreater than, the energy level, E_(e). However, sinceE_(e)=(E_(n)+E_(B)) and E_(n) is based on the a priori unknown floatingpotential, V_(FPa), precise control of the kinetic energy of the freeelectrons to precisely target the energy level, E_(e), may not bepossible.

Although the floating potential (e.g., V_(FPa) of FIG. 1F) may beempirically and/or experimentally determined for a given process atstable operating conditions of the DC plasma chamber, anyinconsistencies and/or lack of repeatability of such operatingconditions may invalidate the determined floating potential.Furthermore, as different types of processes inherently yield todifferent floating potentials, the task of precisely controlling thekinetic energy of the free electrons to exactly target the energy levelof an atom at the surface of the substrate may not be feasible. As aresult, some prior art implementations impart kinetic energies onto theatoms at the surface of the substrate that may be substantially largerthan a target atom energy level, and therefore may not allow forselectivity (as atoms of different materials/compositions havingdifferent energy levels may equally be subjected to energy levelssufficient to break their orbital bonds). The electron enhanced materialprocessing (EEMP) according to the teachings of the present disclosureovercome such shortcoming and therefore allow precise control of thekinetic energy of the free electrons to exactly and selectively targetthe energy level of an atom at the surface of the substrate.

FIG. 2A shows a simplified schematic view of a DC plasma processingsystem (200A) according to an embodiment of the present disclosurecomprising means (250, 260) to control the surface potential of thestage, S, when electrically isolated. In other words, the means (250,260) allow for adjustment of the floating potential, V_(FP). As shown inFIG. 2A, the means (250, 260) include an adjustable DC voltage source(250) that is coupled to the anode, A, of the DC plasma reaction chamber(110), and a DC current source (260) that is coupled to the cathode, C,of the DC plasma reaction chamber (110). Accordingly, the potential,V_(A), of the anode, A, may be controlled to be in a range from zerovolts and upward (positive) with respect to the reference ground (Gnd atzero volts), and a (drain) current, Ip, that flows between the anode, A,and the cathode, C, through the reaction chamber (110) can be set by theDC current source (260). Accordingly, the potential, V_(C), of thecathode, C, is not forced by an external DC voltage source (e.g., 150 ofFIG. 1D), rather (is floating and) settles to a (negative) voltage thatis based on the adjustable potential V_(A) of the anode A, and the setcurrent, Ip. Such configuration allows to independently control/adjustthe floating potential, V_(FP), while maintaining the set current, Ip,through the reaction chamber (110) constant to establish and maintain ahigher level of process stability and optimization.

FIG. 2B shows two graphs representative of control of the surfacepotential, V_(FP), of the stage, S, for the DC plasma processing system(200A) described above with reference to FIG. 2A. In particular, FIG. 2Bshows two graphs distinguished by use of solid or dashed lines, eachrepresenting the variation of the plasma potential, V_(PP), across thelongitudinal extension, X, of the chamber (110) for two differentvoltages (V_(A1), V_(A2)) applied to the anode, A, by the adjustable DCvoltage source (250). As can be seen in FIG. 2B, for a positive stepincrease, +ΔV₁₂, of the anode potential from the voltage V_(A1) to thevoltage V_(A2), the floating potential (V_(FP1), V_(FP2)) and thecathode potential (V_(C1), V_(C2)) increase by the same positive step,+ΔV₁₂. As a matter of fact, as shown in FIG. 2B, the entirety of plasmapotential, V_(PP), curve shifts positive by the step +ΔV₁₂. In otherwords, for any longitudinal coordinate, X, in the range [X_(C), X_(A)],a corresponding plasma potential, V_(PP)(X), follows the step increase,+ΔV₁₂. The same behavior applies to negative step variations applied tothe anode, A, by the adjustable DC voltage source (250). In other words,control of the anode, A, potential by the adjustable DC voltage sourcelinearly affects the plasma potential, V_(PP), at any longitudinalcoordinate, X, and therefore, linearly affects the floating potential,V_(FP), and the voltage, V_(S), atop the stage, S, As later described inthe present disclosure, such linearity can be used in the EEMP systemaccording to the present teachings to implement a closed loop controlsubsystem to automatically control the value of the floating potential,V_(FP), to a preset value (e.g., zero volts) while operating the DCplasma chamber for different types of material processing.

FIG. 2C shows two graphs similar to the graphs described above withreference to FIG. 2B, including a specific case where the anode voltage,V_(A1), is equal to zero volts (solid lines). As can be seen in FIG. 2B,the floating potential voltage for such case is equal to a negativevalue, V_(FP1), and therefore negative with respect to (below) theplasma potential, V_(PP). Furthermore, as can be seen in FIG. 2C, for apositive step increase, +ΔV₁₃=(V_(A1)−V_(FP1)), of the anode potential,the floating potential can be adjusted to a value, V_(FP3), that isequal to zero volts. According to an embodiment of the presentdisclosure, such zeroing of the floating potential, V_(FP), may allowprecise control of the kinetic energy of free electrons in the DC plasmato exactly (and selectively) target energy levels of atoms at thesurface of a substrate (whether conductive or insulating) beingprocessed. In other words, and with reference back to FIG. 1F, the apriori unknown floating potential that determines the energy level,E_(n), of a nucleus of an atom targeted/selected for processing isremoved by zeroing of the floating potential, V_(FP). In turn, as shownin FIG. 4B later described, this allows to reference the energy level,E_(e), of target electrons, the kinetic energy level of the freeelectrons in the DC plasma (e.g., V_(KEa) of FIG. 1F), and the biasingvoltage, V_(B), applied to the stage, S, to the same known and fixedreference of zero volts potential, Gnd.

FIG. 3A shows a simplified schematic view of a DC plasma processingsystem (300A) according to an embodiment of the present disclosurecomprising means (250, 260 of FIG. 2A) to control a surface potential ofthe stage, S, and means (R, 311, V_(R) of FIG. 3A) to measure thesurface potential, V_(S) (e.g., floating potential, V_(FP)) atop thestage. As understood by a person skilled in the art, the system (300A)represents an improvement over the system (200A) described above withreference to FIG. 2A by adding the means (R, 311, V_(R)) to measure thesurface potential, V_(S), or in other words, to measure the (surface)floating potential, V_(FP) atop the stage. By enabling such measurementof the floating potential, V_(FP), adjustment of the DC voltage source(250) as described above with reference to FIGS. 2A-2C may be performedwhile monitoring/measuring the surface potential, V_(FP). This in turnallows precise control of the floating potential, V_(FP), including, forexample, to zero such potential (V_(FP)=0 volts).

With continued reference to FIG. 3A, the means (R, 311, V_(R)) includesa reference plate, R, that is placed within DC plasma chamber (110) at asame (longitudinal coordinate) segment [X_(G31), X_(G32)] as the stage,S. The reference plate, R, may be fabricated from any conductivematerial capable of withstanding (internal) operating conditions of thechamber (110), and may have any planar shape, including planar shapesaccording to, for example, a square, rectangle, circle, pentagon,trapezoid or other. Because the reference plate, R, is arranged in thesame region of the plate, S, and therefore in a region of a samesubstantially constant plasma potential, V_(PP), the reference plate, R,sees a same floating potential, V_(FP), as the stage, S. In other words,by measuring the (surface) potential, V_(R), at the reference plate, R,the floating potential at the stage, S, can be determined. An insulatedconductive wire (311) attached to the reference plate, R, may be used toroute/couple the potential, V_(R), to measurement electronics (e.g.,transducer) placed outside the chamber (110). It should be noted thatsuch measurement electronics should not provide a DC current path to theplasma through plate R.

With continued reference to FIG. 3A, placement of the reference plate,R, may be at any longitudinal extension of the chamber (110) within thesegment [X_(G31), X_(G32)] that is technically feasible and practical.As the chamber, S, may include an access door adjacent the stage, S, onone side of the chamber (110), in some exemplary embodiments thereference plate, R, may be arranged against, or in the vicinity, of awall of the chamber (110) that is on an opposite side of the access doorand stage, S. Furthermore, according to an exemplary embodiment, acenter of the reference plate, R, and a center of the stage, S, (e.g.,intersection of the two segments that make the T shape of the stage asshown in the figures) may be contained within a line that isperpendicular to the axial direction (e.g., centerline, direction oflongitudinal extension) of the chamber (110). Applicants of the presentdisclosure have verified high accuracy of the means (R, 311, V_(R)) intracking of the floating potential of the stage, S.

FIG. 3B shows a simplified schematic view of a DC plasma processingsystem (300B) according to an embodiment of the present disclosure thatis based on the system (300A) of FIG. 3A with added means (320, CT) forautomatic control of the surface potential, V_(FP), at the stage, S. Themeans (320, CT) includes control electronics (320) configured toimplement a closed loop control system to automatically control thevalue of the floating potential, V_(FP), at the stage, S, to a presetvalue (e.g., zero volts) while operating the DC plasma chamber fordifferent types of processing. In particular, as shown in FIG. 3B, thecontrol electronics (320) takes the (surface) potential, V_(R), of thereference plate, R, as input via a coupling provided by the insulatedconductive wire (311), and generates therefrom a control (error) signal,CT, to the adjustable DC voltage source (250) to adjust the voltage,V_(A), provided to the anode, A, and therefore, as described above withreference to FIGS. 2A-2C, adjust the floating potential, V_(FP), at thestage, S. The control (error) signal, CT, may be generated with respectto a desired target/preset value of the floating potential, V_(FP), suchas, for example, zero volts. A person skilled in the art is well awareof design techniques for implementing the control electronics (320)which are outside the scope of the present disclosure. In particular, aperson skilled in the art is well aware of using operational amplifiersor error amplifiers in such control electronics (320), wherein inputs ofsuch amplifiers may be coupled to the potential, V_(R), and to thedesired target/preset value (e.g., zero volts) of the floatingpotential, V_(FP), to generate an error signal (e.g., CT) based on adifference of the inputs.

FIG. 4A shows a simplified schematic view of a DC plasma processingsystem (400A) according to an embodiment of the present disclosure thatis based on the system of FIG. 3B with added biasing means (C_(S), 480)for biasing of the stage, S. In particular, the biasing means (C_(S),480) includes a biasing signal generator (480) that is coupled to thestage, S, through a capacitor, C_(S), of the biasing means. In otherwords, a biasing signal, V_(B), generated at an output of the biasingsignal generator (480) is capacitively coupled to the stage, S, throughthe capacitor, C_(S). As previously described in the present disclosure,such capacitive coupling may allow removal of any DC current path fromor into the DC plasma chamber (110), thereby preventing any undesiredperturbation of operating conditions of the chamber (110). It should benoted that the biasing signal generator (480) may include, for example,a programmable waveform generator configured to output a waveform of thebiasing signal, V_(B), according to desired characteristics, includingfor example, amplitude, frequency, duty cycle and/or rising/fallingedges/slopes. It is further noted that the stage, S, may include a firstconductive portion (e.g., vertical lead connected to the capacitorC_(S)) for electrical coupling of the biasing signal, V_(B), to thestage, S, and a second portion of the stage (e.g., horizontal supportplate) that may include conductive and/or insulating material.

FIG. 4B shows an exemplary biasing signal, V_(B1), provided to thestage, S, of the DC plasma processing system (400A) of FIG. 4A and acorresponding surface potential, V_(S), generated at the surface of thestage, S. As can be clearly understood by a person skilled in the art,the graphs shown in FIG. 4B correspond to a configuration of the system(400) wherein the floating potential, V_(FP), is adjusted or controlledto be at zero volts. Accordingly, and in view of (or in contrast to) theabove description with reference to FIG. 1E, the (kinetic) energy of thefree electrons and/or ions attracted to the surface of the stage, S, ora substrate thereupon, is based on the potential differenceV_(KE)=(V_(B1)−ΔV_(FP)), with ΔV_(FP)=(V_(PP)−V_(FP)). Accordingly,since in practical substrate processing applications using a DC plasmachamber, a value of ΔV_(FP) may be substantially smaller (e.g., ratio of1/50 or smaller) than the value of V_(KE) (e.g., based on the energylevel E_(e) of a target electron per FIG. 4C); an approximationV_(KE)=V_(B1) may be considered reasonable. In turn, this allows asimple and straightforward generation of the biasing signal, V_(B1),provided to the stage, S, for implementation of the electron enhancedmaterial processing (EEMP) according to the teachings of the presentdisclosure that exactly and selectively targets the energy level of anatom (e.g., bound electron) at the surface of the substrate.

With further reference to FIG. 4A and FIG. 4B, it is noted thatexcitation of the energy levels of the atoms at the surface of thestage, S, or at the surface of a substrate arranged atop the stage, S,may be primarily based on an instantaneous change in the surfacepotential, V_(S). Accordingly, excitation of the energy levels may beaccomplished immediately at the end of the transition of the biasingvoltage to the target value, V_(B1), or in other words, at the end ofthe slope shown in FIG. 4B.

FIG. 4C shows exemplary energy levels of atoms at a surface of thestage, S, of the of the DC plasma processing system (400A) of FIG. 4A.FIG. 4C highlights benefits of the electron enhanced material processing(EEMP) according to the teachings of the present disclosure that allowsadjustments to exactly and selectively target the energy level of anatom (e.g., Ee≈V_(KE) per FIG. 4C) at the surface of the substrate basedon the zeroing of the floating potential, V_(FP), according the abovedescription with reference to FIGS. 2A-2C, further based on thereference plate, R, according to above description with reference toFIG. 3A, further based on the (optional) closed loop control systemprovided by the control electronics (320) according to the abovedescription with reference to FIG. 3B, and further based on thecapacitive coupling of the biasing signal, V_(B), provided by thebiasing signal generator (480) according to the above description withreference to FIG. 4A.

FIG. 5 is a process chart (500) showing various steps of a methodaccording to an embodiment of the present disclosure for processing asurface of a substrate. As shown in FIG. 5 , such steps comprise:placing a substrate support stage in a region of a DC plasma reactionchamber configured to produce a positive column of the DC plasma,according to step (510); generating a DC plasma by coupling anadjustable DC voltage source and a DC current source respectively to ananode and a cathode of the DC plasma reaction chamber, according to step(520); based on the generating, producing a floating potential at asurface of the substrate support stage, according to step (530);adjusting a potential at the anode via the adjustable DC voltage sourcewhile maintaining via the DC current source a constant DC currentbetween the anode and the cathode, according to step (540); and based onthe adjusting and the maintaining, setting the floating potential to apotential of a reference ground of the adjustable DC voltage source,according to step (550).

A number of embodiments of the disclosure have been described.Nevertheless, it will be understood that various modifications may bemade without departing from the spirit and scope of the presentdisclosure. Accordingly, other embodiments are within the scope of thefollowing claims.

The examples set forth above are provided to those of ordinary skill inthe art as a complete disclosure and description of how to make and usethe embodiments of the disclosure and are not intended to limit thescope of what the inventor/inventors regard as their disclosure.

Modifications of the above-described modes for carrying out the methodsand systems herein disclosed that are obvious to persons of skill in theart are intended to be within the scope of the following claims. Allpatents and publications mentioned in the specification are indicativeof the levels of skill of those skilled in the art to which thedisclosure pertains. All references cited in this disclosure areincorporated by reference to the same extent as if each reference hadbeen incorporated by reference in its entirety individually.

It is to be understood that the disclosure is not limited to particularmethods or systems, which can, of course, vary. It is also to beunderstood that the terminology used herein is for the purpose ofdescribing particular embodiments only and is not intended to belimiting. As used in this specification and the appended claims, thesingular forms “a,” “an,” and “the” include plural referents unless thecontent clearly dictates otherwise. The term “plurality” includes two ormore referents unless the content clearly dictates otherwise. Unlessdefined otherwise, all technical and scientific terms used herein havethe same meaning as commonly understood by one of ordinary skill in theart to which the disclosure pertains.

1. A method for processing a surface of a substrate, the methodcomprising: processing the substrate via a direct-current (DC) plasmasystem, wherein the DC plasma system comprises: a DC plasma reactionchamber configured to contain a DC plasma that is generated between ananode and a cathode of the DC plasma reaction chamber; an adjustable DCvoltage source having an output that is electrically coupled to theanode; a DC current source that is electrically coupled to the cathode;and a substrate support stage arranged in a region of the DC plasmareaction chamber that contains a positive column of the DC plasma,wherein the adjustable DC voltage source and the DC current source areelectrically coupled to a reference ground, and the DC current source isconfigured to set, during the processing of the substrate, a constant DCcurrent that flows between the anode and the cathode, and the adjustableDC voltage source is configured to adjust, during the processing of thesubstrate and independently from the constant DC current, an electricalpotential at the anode to set a substrate floating potential at asurface of the substrate support stage to a potential of the referenceground.
 2. The method according to claim 1, wherein: the constant DCcurrent is configured to generate the DC plasma.
 3. The method accordingto claim 2, wherein: an electrical potential at the cathode settles to apotential that is based on the electrical potential at the anode and theconstant DC current, and a positive or negative step change of theelectrical potential at the anode causes a same positive or negativestep change of the electrical potential at the cathode.
 4. The methodaccording to claim 1, wherein the DC plasma system further comprises:control electronics configured to generate an error signal based on adifference between the substrate floating potential and the potential ofthe reference ground.
 5. The method according to claim 4, wherein: thecontrol electronics is electrically coupled to a reference plate made ofa conductive material arranged in the region of the DC plasma reactionchamber that contains the positive column so that a surface potential ofthe reference plate is equal to the substrate floating potential.
 6. Themethod according to claim 4, wherein: the adjustable DC voltage sourceis configured to receive the error signal and adjust the electricalpotential at the anode based on a value of the error signal.
 7. Themethod according to claim 5, wherein: the adjustable DC voltage source,the reference plate and the control electronics are configured toprovide a closed loop control system to maintain the substrate floatingpotential to the potential of the reference ground.
 8. The methodaccording to claim 1, wherein the DC plasma system further comprises: abiasing signal generator that is capacitively coupled to the substratesupport stage, wherein the biasing signal generator is configured togenerate a biasing signal having a voltage level that is referenced tothe potential of the reference ground, the biasing signal capacitivelycoupled to the substrate support stage, and the biasing signal isconfigured to control a surface potential of the substrate supportstage.
 9. The method according to claim 8, wherein: the biasing signalgenerator is configured to control waveform characteristics of thebiasing signal, the waveform characteristics comprising the voltagelevel, a frequency, a duty cycle, a rising edge, or a falling edge. 10.The method according to claim 8, wherein: when the voltage level of thebiasing signal is zero volts, the surface potential of the substratesupport stage is at zero volts, the energy level of free electrons inthe DC plasma is at zero volts, and the energy level of nuclei of atomsat a surface of the substrate is at zero volts.
 11. The method accordingto claim 10, wherein: when the voltage level of the biasing signal isincreased by a positive voltage step, the surface potential of thesubstrate support stage is increased by the same positive voltage step,and the energy level of the free electrons is increased in proportion tothe positive voltage step.
 12. A method for processing a surface of asubstrate, the method comprising: placing a substrate support stage in aregion of a DC plasma reaction chamber configured to produce a positivecolumn of DC plasma; generating the DC plasma by coupling an adjustableDC voltage source and a DC current source respectively to an anode and acathode of the DC plasma reaction chamber; based on the generating,producing a substrate floating potential at a surface of the substratesupport stage; establishing a constant DC current between the anode andthe cathode via the DC current source; adjusting, independently from theconstant DC current, a potential at the anode via the adjustable DCvoltage source; and based on the adjusting, setting the substratefloating potential to a specific potential relative to a potential of areference ground of the adjustable DC voltage source.
 13. The methodaccording to claim 12, wherein: the specific potential is at thepotential of the reference ground.
 14. The method according to claim 12,wherein: a potential at the cathode settles to a potential that is basedon the establishing and the adjusting, and the adjusting produces apositive or negative step change of the potential at the anode that isequal to a positive or negative step change of the potential at thecathode.
 15. The method according to claim 12, further comprising:measuring the substrate floating potential; and based on the measuring,generating an error signal based on a difference between the substratefloating potential and the potential of the reference ground.
 16. Themethod according to claim 15, further comprising: arranging a referenceplate made of a conductive material in a region of the positive column;based on the arranging, obtaining a surface potential of the referenceplate that is equal to the substrate floating potential; and measuringthe substrate floating potential by measuring the surface potential ofthe reference plate.
 17. The method according to claim 16, furthercomprising: generating an error signal based on a difference between thesurface potential of the reference plate and the potential of thereference ground.
 18. The method according to claim 12, furthercomprising: generating an error signal based on a difference between thesubstrate floating potential and the potential of the reference ground.19. The method according to claim 18, further comprising: furtheradjusting, via the adjustable DC voltage source, the potential at theanode based on a value of the error signal while maintaining theconstant DC current source via a same setting of the DC current source.20. The method according to claim 12, further comprising: placing asubstrate on the substrate support stage; capacitively coupling abiasing signal to the substrate support stage, thereby energizing freeelectrons in the DC plasma; based on the energizing, accelerating thefree electrons onto a surface of the substrate; and based on theaccelerating, colliding the free electrons with atoms at the surface ofthe substrate, thereby breaking energy bonds between electrons andnuclei of the atoms, wherein a voltage level of the biasing signal isselected to target a specific energy level of the electrons of theatoms, the atoms making up a specific material.